I'll never forget, a family friend said that when they had just met us, my little brother (about 6 years old at the time) told them "My dad drives a Mercedes." They wondered if we were rich or something, but I'm sure when they found out it was a fifteen year old diesel the picture became a little clearer.
I would only feel guilty about driving a car if I knew that in some way I was doing it in an attempt to out-class people. I have absolutely no qualms about flashing any moniker, be it Ford, Mercedes, Honda, or whatever. Obviously you have to be prepared to deal with whatever preconceptions people have about certain cars (BMW = aggressive "big shot" driver, for example). I have no problem if it makes me look richer than I am though, as long as it's not actually costing me.

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Once and future king:
'64 Ford Fairlane w/approx 238,000 - looks rough, but amazingly reliable if you know how to look after it; I will soon begin work to totally restore and modernize it.
Family vehicles that I lay some claim to:
'78 300D w/approx 350,000 original, '62 Ford F100 4x4, '90 Ford E150 w/171,000 original